A protection cap of an optical connector disclosed in Patent Literature 1 includes U-shaped optical fiber molded with synthetic resin or the like so as to expose both ends of the fiber from a mold part. The protection cap is attachable and detachable to an optical connector including a light emitting device and a light receiving device arranged at a device side. Since the protection cap inhibits dust from entering the optical connector and an optical signal from a light emitting device is input to the light receiving device via the optical fiber of the protection cap, the device can be tested (for example, see Patent Literature 1, specification p. 5, line 3 to p. 6, line 1, FIG. 1).